Version: Config V2

Rust SDK Reference

Getting started

1. Install the package

Run the following Cargo command in your project directory:

cargo add configcat

Or add the following to your Cargo.toml:

[dependencies]
configcat = "0.1"

2. Import the `configcat` module to your application

use configcat::*;

3. Create the ConfigCat client with your SDK Key

use configcat::*;

#[tokio::main]
async fn main() {
    let client = Client::new("#YOUR-SDK-KEY#").unwrap();
}

4. Get your setting value

use configcat::*;

#[tokio::main]
async fn main() {
    let client = Client::new("#YOUR-SDK-KEY#").unwrap();

    let is_awesome_feature_enabled = client.get_value("isAwesomeFeatureEnabled", false, None).await;
    
    if is_awesome_feature_enabled {
        do_the_new_thing();
    } else {
        do_the_old_thing();
    }
}

Creating the ConfigCat Client

ConfigCat Client is responsible for:

managing the communication between your application and ConfigCat servers.
caching your setting values and feature flags.
serving values quickly in a failsafe way.

Client::new(<sdk_key>) returns a client with default options.

Arguments	Description
`sdk_key`	SDK Key to access your feature flags and configurations. Get it from ConfigCat Dashboard.

Custom client options

Client::builder(<sdk_key>) returns a builder used to construct a customized client.

use std::time::Duration;
use configcat::{Client, PollingMode, DataGovernance};

let builder = Client::builder("#YOUR-SDK-KEY#")
    .polling_mode(PollingMode::AutoPoll(Duration::from_secs(60)))
    .data_governance(DataGovernance::EU);

let client = builder.build().unwrap();

Available options:

Option	Description
`data_governance(DataGovernance)`	Defaults to `Global`. Describes the location of your feature flag and setting data within the ConfigCat CDN. This parameter needs to be in sync with your Data Governance preferences. More about Data Governance. Available options: `Global`, `EuOnly`.
`base_url(&str)`	Sets the CDN base url (forward proxy, dedicated subscription) from where the sdk will download the configurations.
`cache(Box<dyn ConfigCache>)`	Sets a custom cache implementation for the client. See below.
`http_timeout(Duration)`	Sets the maximum wait time for a HTTP response. More about the HTTP timeout
`polling_mode(PollingMode)`	Defaults to `AutoPoll`. Sets the polling mode for the client. More about polling modes.
`overrides(Box<dyn OverrideDataSource>, OverrideBehavior)`	Sets the local feature flag & setting overrides. More about feature flag overrides.
`default_user(User)`	Sets the default user. More about default user.
`offline(bool)`	Defaults to `false`. Indicates whether the SDK should be initialized in offline mode. More about offline mode.

caution

We strongly recommend you to use the ConfigCat Client as a Singleton object in your application. If you want to use multiple SDK Keys in the same application, create only one ConfigCat Client per SDK Key.

Anatomy of `get_value()`

Parameters	Description
`key`	REQUIRED. Setting-specific key. Set on ConfigCat Dashboard for each setting.
`default`	REQUIRED. This value will be returned in case of an error.
`user`	Optional, User Object. Essential when using Targeting. Read more about Targeting.

let is_awesome_feature_enabled = client.get_value(
    "isAwesomeFeatureEnabled", // Setting Key
    false, // Default value
    Some(User::new("#UNIQUE-USER-IDENTIFIER#")) // Optional User Object
).await;

caution

It is important to provide an argument for the default parameter, specifically for the T generic type parameter, that matches the type of the feature flag or setting you are evaluating. Please refer to the following table for the corresponding types.

Setting type mapping

Setting Kind	Type parameter `T`
On/Off Toggle	`bool`
Text	`String`
Whole Number	`i64`
Decimal Number	`f64`

If you specify an allowed type but it mismatches the setting kind, an error message will be logged and default will be returned.

When relying on type inference and not explicitly specifying the type parameter, be mindful of potential type mismatch issues, especially with number types. For example, client.get_value("keyOfMyDecimalSetting", 0, None).await will return default (0) instead of the actual value of the decimal setting because the compiler infers the type as i64 instead of f64, that is, the call is equivalent to client.get_value::<i64>("keyOfMyDecimalSetting", 0, None).await, which is a type mismatch.

To correctly evaluate a decimal setting, you should use:

let value = client.get_value("keyOfMyDecimalSetting", 0.0, None).await;
// -or-
let value = client.get_value("keyOfMyDecimalSetting", 0_f64, None).await;

Anatomy of `get_value_details()`

get_value_details() is similar to get_value() but instead of returning the evaluated value only, it provides more detailed information about the evaluation result.

Parameters	Description
`key`	REQUIRED. Setting-specific key. Set on ConfigCat Dashboard for each setting.
`default`	REQUIRED. This value will be returned in case of an error.
`user`	Optional, User Object. Essential when using Targeting. Read more about Targeting.

let user = User::new("#UNIQUE-USER-IDENTIFIER#"); // Optional User Object
let details = client.get_value_details("keyOfMyFeatureFlag", false, Some(user)).await;

caution

The details result contains the following information:

Field	Type	Description
`key`	`String`	The key of the evaluated feature flag or setting.
`value`	`bool` / `String` / `i64` / `f64`	The evaluated value of the feature flag or setting.
`user`	`Option<User>`	The User Object used for the evaluation.
`is_default_value`	`bool`	True when the default value passed to `GetValueDetailsAsync()` is returned due to an error.
`error`	`Option<ClientError>`	In case of an error, this field contains the related error structure.
`matched_targeting_rule`	`Option<Arc<TargetingRule>>`	The Targeting Rule (if any) that matched during the evaluation and was used to return the evaluated value.
`matched_percentage_option`	`Option<Arc<PercentageOption>>`	The Percentage Option (if any) that was used to select the evaluated value.
`fetch_time`	`Option<DateTime<Utc>>`	The last download time (UTC) of the current config.

User Object

The User Object is essential if you'd like to use ConfigCat's Targeting feature.

let user = User::new("#UNIQUE-USER-IDENTIFIER#");

let user = User::new("[email protected]");

Option	Description
`new(<identifier>)`	REQUIRED. Unique identifier of a user in your application. Can be any `string` value, even an email address.
`email(&str)`	Optional email address for easier Targeting Rule definitions.
`country(&str)`	Optional country for easier Targeting Rule definitions.
`custom(&str, Into<UserValue>)`	Optional custom attribute of a user for advanced Targeting Rule definitions. E.g. User role, Subscription type.

let user = new User("#UNIQUE-USER-IDENTIFIER#")
    .email("[email protected]")
    .country("United Kingdom")
    .custom("SubscriptionType", "Pro")
    .custom("UserRole", "Admin");

The custom() method allows attribute values other than String:

let user = new User("#UNIQUE-USER-IDENTIFIER#")
    .custom("Rating", 4.5)
    .custom("RegisteredAt", DateTime::from_str("2023-06-14T15:27:15.8440000Z").unwrap())
    .custom("Roles", ["Role1", "Role2"]);

User Object Attribute Types

All comparators support String values as User Object attribute (in some cases they need to be provided in a specific format though, see below), but some of them also support other types of values. It depends on the comparator how the values will be handled. The following rules apply:

Text-based comparators (EQUALS, IS ONE OF, etc.)

accept String values,
all other values are automatically converted to String (a warning will be logged but evaluation will continue as normal).

SemVer-based comparators (IS ONE OF, <, >=, etc.)

accept String values containing a properly formatted, valid semver value,
all other values are considered invalid (a warning will be logged and the currently evaluated targeting rule will be skipped).

Number-based comparators (=, <, >=, etc.)

accept Int, UInt, or Float values,
accept String values containing a properly formatted, valid Float value,
all other values are considered invalid (a warning will be logged and the currently evaluated targeting rule will be skipped).

Date time-based comparators (BEFORE / AFTER)

accept DateTime values, which are automatically converted to a second-based Unix timestamp,
accept Int, UInt, or Float values representing a second-based Unix timestamp,
accept String values containing a properly formatted, valid Float value,
all other values are considered invalid (a warning will be logged and the currently evaluated targeting rule will be skipped).

String array-based comparators (ARRAY CONTAINS ANY OF / ARRAY NOT CONTAINS ANY OF)

accept Vec of Strings,
accept String values containing a valid JSON string which can be deserialized to an array of String,
all other values are considered invalid (a warning will be logged and the currently evaluated targeting rule will be skipped).

Default user

It's possible to set a default User Object that will be used on feature flag and setting evaluation. It can be useful when your application has a single user only or rarely switches users.

You can set the default User Object either on SDK initialization:

let client = Client::builder("#YOUR-SDK-KEY#")
    .default_user(User::new("[email protected]"))
    .build()
    .unwrap();

...or using the set_default_user() method of the configcat::Client:

client.set_default_user(User::new("[email protected]"));

Whenever the evaluation methods like get_value(), get_value_details(), etc. are called without an explicit user parameter, the SDK will automatically use the default user as a User Object.

let client = Client::builder("#YOUR-SDK-KEY#")
    .default_user(User::new("[email protected]"))
    .build()
    .unwrap();

// The default user will be used in the evaluation process.
let value = client.get_value("keyOfMyFeatureFlag", false, None).await;

When a user parameter is passed to the evaluation methods, it takes precedence over the default user.

let client = Client::builder("#YOUR-SDK-KEY#")
    .default_user(User::new("[email protected]"))
    .build()
    .unwrap();

let other_user = User::new("[email protected]");

// other_user will be used in the evaluation process.
let value = client.get_value("keyOfMyFeatureFlag", false, Some(other_user)).await;

You can also remove the default user by doing the following:

client.clear_default_user();

Polling Modes

The ConfigCat SDK supports 3 different polling mechanisms to acquire the setting values from ConfigCat. After latest setting values are downloaded, they are stored in the local cache, then all get_value() calls are served from there. With the following polling modes, you can customize the SDK to best fit to your application's lifecycle. More about polling modes & caching.

When no polling mode is specified upon SDK initialization, AutoPoll will be selected with a 60s poll interval.

Auto polling (default)

The ConfigCat SDK downloads and stores the latest values automatically. The Duration parameter specifies how frequent the config JSON downloads will happen.

let client = Client::builder("#YOUR-SDK-KEY#")
    .polling_mode(PollingMode::AutoPoll(Duration::from_secs(60)))
    .build()
    .unwrap();

Lazy loading

When calling get_value(), the ConfigCat SDK downloads the latest setting values if they are not present or expired in the cache. In this case get_value() will return the setting value after the cache is updated. The Duration parameter specifies after how much time the cache is considered stale.

let client = Client::builder("#YOUR-SDK-KEY#")
    .polling_mode(PollingMode::LazyLoad(Duration::from_secs(60)))
    .build()
    .unwrap();

Manual polling

Manual polling gives you full control over when the config JSON (with the setting values) is downloaded. ConfigCat SDK will not update them automatically. Calling refresh() is your application's responsibility.

let client = Client::builder("#YOUR-SDK-KEY#")
    .polling_mode(PollingMode::Manual)
    .build()
    .unwrap();

_ = client.refresh().await;

get_value() returns default if the cache is empty. Call refresh() to update the cache.

Online / Offline mode

In cases where you want to prevent the SDK from making HTTP calls, you can switch it to offline mode:

client.offline();

In offline mode, the SDK won't initiate HTTP requests and will work only from its cache.

To switch the SDK back to online mode, do the following:

client.online();

Using the client.is_offline() method, you can check whether the SDK is in offline mode.

Flag Overrides

With flag overrides you can overwrite the feature flags & settings downloaded from the ConfigCat CDN with local values. Moreover, you can specify how the overrides should apply over the downloaded values. The following 3 behaviours are supported:

Local only (OverrideBehavior::LocalOnly): When evaluating values, the SDK will not use feature flags & settings from the ConfigCat CDN, but it will use all feature flags & settings that are loaded from local-override sources.
Local over remote (OverrideBehavior::LocalOverRemote): When evaluating values, the SDK will use all feature flags & settings that are downloaded from the ConfigCat CDN, plus all feature flags & settings that are loaded from local-override sources. If a feature flag or a setting is defined both in the downloaded and the local-override source then the local-override version will take precedence.
Remote over local (OverrideBehavior::RemoteOverLocal): When evaluating values, the SDK will use all feature flags & settings that are downloaded from the ConfigCat CDN, plus all feature flags & settings that are loaded from local-override sources. If a feature flag or a setting is defined both in the downloaded and the local-override source then the downloaded version will take precedence.

You can load your feature flag & setting overrides from a file or from a simple HashMap<String, configcat::Value>.

JSON File

The SDK can load your feature flag & setting overrides from a file.

File

use configcat::{Client, FileDataSource, OverrideBehavior};

let file_ds = FileDataSource::new("path/to/local_flags.json").unwrap();

let client = Client::builder("localhost")
    .overrides(Box::new(file_ds), OverrideBehavior::LocalOnly)
    .build()
    .unwrap();

JSON File Structure

The SDK supports 2 types of JSON structures to describe feature flags & settings.

1. Simple (key-value) structure

{
  "flags": {
    "enabledFeature": true,
    "disabledFeature": false,
    "intSetting": 5,
    "doubleSetting": 3.14,
    "stringSetting": "test"
  }
}

2. Complex (full-featured) structure

This is the same format that the SDK downloads from the ConfigCat CDN. It allows the usage of all features that are available on the ConfigCat Dashboard.

You can download your current config JSON from ConfigCat's CDN and use it as a baseline.

A convenient way to get the config JSON for a specific SDK Key is to install the ConfigCat CLI tool and execute the following command:

configcat config-json get -f v6 -p {YOUR-SDK-KEY} > config.json

(Depending on your Data Governance settings, you may need to add the --eu switch.)

Alternatively, you can download the config JSON manually, based on your Data Governance settings:

GLOBAL: https://cdn-global.configcat.com/configuration-files/{YOUR-SDK-KEY}/config_v6.json
EU: https://cdn-eu.configcat.com/configuration-files/{YOUR-SDK-KEY}/config_v6.json

{
  "p": {
    // hash salt, required only when confidential text comparator(s) are used
    "s": "80xCU/SlDz1lCiWFaxIBjyJeJecWjq46T4eu6GtozkM="
  },
  "s": [ // array of segments
    {
      "n": "Beta Users", // segment name
      "r": [ // array of User Conditions (there is a logical AND relation between the elements)
        {
          "a": "Email", // comparison attribute
          "c": 0, // comparator (see below)
          "l": [ // comparison value (see below)
            "[email protected]", "[email protected]"
          ]
        }
      ]
    }
  ],
  "f": { // key-value map of feature flags & settings
    "isFeatureEnabled": { // key of a particular flag / setting
      "t": 0, // setting type, possible values:
              // 0 -> on/off setting (feature flag)
              // 1 -> text setting
              // 2 -> whole number setting
              // 3 -> decimal number setting
      "r": [ // array of Targeting Rules (there is a logical OR relation between the elements)
        {
          "c": [ // array of conditions (there is a logical AND relation between the elements)
            {
              "u": { // User Condition
                "a": "Email", // comparison attribute
                "c": 2, // comparator, possible values and required comparison value types:
                        // 0  -> IS ONE OF (cleartext) + string array comparison value ("l")
                        // 1  -> IS NOT ONE OF (cleartext) + string array comparison value ("l")
                        // 2  -> CONTAINS ANY OF (cleartext) + string array comparison value ("l")
                        // 3  -> NOT CONTAINS ANY OF (cleartext) + string array comparison value ("l")
                        // 4  -> IS ONE OF (semver) + semver string array comparison value ("l")
                        // 5  -> IS NOT ONE OF (semver) + semver string array comparison value ("l")
                        // 6  -> < (semver) + semver string comparison value ("s")
                        // 7  -> <= (semver + semver string comparison value ("s")
                        // 8  -> > (semver) + semver string comparison value ("s")
                        // 9  -> >= (semver + semver string comparison value ("s")
                        // 10 -> = (number) + number comparison value ("d")
                        // 11 -> <> (number + number comparison value ("d")
                        // 12 -> < (number) + number comparison value ("d")
                        // 13 -> <= (number + number comparison value ("d")
                        // 14 -> > (number) + number comparison value ("d")
                        // 15 -> >= (number) + number comparison value ("d")
                        // 16 -> IS ONE OF (hashed) + string array comparison value ("l")
                        // 17 -> IS NOT ONE OF (hashed) + string array comparison value ("l")
                        // 18 -> BEFORE (UTC datetime) + second-based Unix timestamp number comparison value ("d")
                        // 19 -> AFTER (UTC datetime) + second-based Unix timestamp number comparison value ("d")
                        // 20 -> EQUALS (hashed) + string comparison value ("s")
                        // 21 -> NOT EQUALS (hashed) + string comparison value ("s")
                        // 22 -> STARTS WITH ANY OF (hashed) + string array comparison value ("l")
                        // 23 -> NOT STARTS WITH ANY OF (hashed) + string array comparison value ("l")
                        // 24 -> ENDS WITH ANY OF (hashed) + string array comparison value ("l")
                        // 25 -> NOT ENDS WITH ANY OF (hashed) + string array comparison value ("l")
                        // 26 -> ARRAY CONTAINS ANY OF (hashed) + string array comparison value ("l")
                        // 27 -> ARRAY NOT CONTAINS ANY OF (hashed) + string array comparison value ("l")
                        // 28 -> EQUALS (cleartext) + string comparison value ("s")
                        // 29 -> NOT EQUALS (cleartext) + string comparison value ("s")
                        // 30 -> STARTS WITH ANY OF (cleartext) + string array comparison value ("l")
                        // 31 -> NOT STARTS WITH ANY OF (cleartext) + string array comparison value ("l")
                        // 32 -> ENDS WITH ANY OF (cleartext) + string array comparison value ("l")
                        // 33 -> NOT ENDS WITH ANY OF (cleartext + string array comparison value ("l")
                        // 34 -> ARRAY CONTAINS ANY OF (cleartext) + string array comparison value ("l")
                        // 35 -> ARRAY NOT CONTAINS ANY OF (cleartext) + string array comparison value ("l")
                "l": [ // comparison value - depending on the comparator, another type of value may need
                       // to be specified (see above):
                       // "s": string
                       // "d": number
                  "@example.com"
                ]
              }
            },
            {
              "p": { // Flag Condition (Prerequisite)
                "f": "mainIntFlag", // key of prerequisite flag
                "c": 0, // comparator, possible values: 0 -> EQUALS, 1 -> NOT EQUALS
                "v": { // comparison value (value's type must match the prerequisite flag's type)
                  "i": 42
                }
              }
            },
            {
              "s": { // Segment Condition
                "s": 0, // segment index, a valid index into the top-level segment array ("s")
                "c": 1 // comparator, possible values: 0 -> IS IN SEGMENT, 1 -> IS NOT IN SEGMENT
              }
            }
          ],
          "s": { // alternatively, an array of Percentage Options ("p", see below) can also be specified
            "v": { // the value served when the rule is selected during evaluation
              "b": true
            },
            "i": "bcfb84a7"
          }
        }
      ],
      "p": [ // array of Percentage Options
        {
          "p": 10, // % value
          "v": { // the value served when the Percentage Option is selected during evaluation
            "b": true
          },
          "i": "bcfb84a7"
        },
        {
          "p": 90,
          "v": {
            "b": false
          },
          "i": "bddac6ae"
        }
      ],
      "v": { // fallback value, served when none of the Targeting Rules match,
             // no Percentage Options are defined or evaluation of these is not possible
        "b": false // depending on the setting type, another type of value may need to be specified:
                   // text setting -> "s": string
                   // whole number setting -> "i": number
                   // decimal number setting -> "d": number
      },
      "i": "430bded3" // variation id (for analytical purposes)
    }
  }
}

For a more comprehensive specification of the config JSON v6 format, you may refer to this JSON schema document.

Map

You can set up the SDK to load your feature flag & setting overrides from a HashMap<String, configcat::Value>.

use configcat::{Client, MapDataSource, OverrideBehavior, Value};

let map: MapDataSource = [
    ("enabledFeature", Value::Bool(true)),
    ("disabledFeature", Value::Bool(false)),
    ("intSetting", Value::Int(5)),
    ("doubleSetting", Value::Float(1.2)),
    ("stringSetting", Value::String("test".to_owned())),
].into();

let client = Client::builder("localhost")
    .overrides(Box::new(map), OverrideBehavior::LocalOnly)
    .build()
    .unwrap();

`get_all_keys()`

You can query the keys of each feature flag and setting with the get_all_keys() method.

let client = Client::new("#YOUR-SDK-KEY#").unwrap();
let keys = client.get_all_keys().await;

`get_all_values()`

Evaluates and returns the values of all feature flags and settings. Passing a User Object is optional.

let client = Client::new("#YOUR-SDK-KEY#").unwrap();
let values = await client.get_all_values(None).await;

// invoke with User Object
let user = User::new("#UNIQUE-USER-IDENTIFIER#");
let values_with_user = await client.get_all_values(Some(user)).await;

`get_all_value_details()`

Evaluates and returns the values along with evaluation details of all feature flags and settings. Passing a User Object is optional.

let client = Client::new("#YOUR-SDK-KEY#").unwrap();
let details = await client.get_all_value_details(None).await;

// invoke with User Object
let user = User::new("#UNIQUE-USER-IDENTIFIER#");
let details_with_user = await client.get_all_value_details(Some(user)).await;

Cache

The ConfigCat SDK stores the downloaded config data in a local cache to minimize network traffic and enhance client performance. If you prefer to use your own cache solution, such as an external or distributed cache in your system, you can implement the ConfigCache trait and call the cache() method of the ClientBuilder with your implementation. This allows you to seamlessly integrate ConfigCat with your existing caching infrastructure.

struct CustomCache {}

impl ConfigCache for CustomCache {
    fn read(&self, key: &str) -> Option<String> {
        // here you have to return with the cached value
    }

    fn write(&self, key: &str, value: &str) {
        // here you have to store the new value in the cache
    }
}

Then use your custom cache implementation:

let client = Client::builder("#YOUR-SDK-KEY#")
    .cache(Box::new(CustomCache{}))
    .build()
    .unwrap();

HTTP Proxy

The SDK uses the reqwest crate for HTTP communication. This crate supports HTTP proxies via the HTTP_PROXY / HTTPS_PROXY environment variables.

HTTP Timeout

You can set the maximum wait time for a ConfigCat HTTP response.

let client = Client::builder("#YOUR-SDK-KEY#")
    .http_timeout(Duration::from_secs(60));
    .build()
    .unwrap();

The default timeout is 30 seconds.

Logging

The SDK uses the log crate for logging, so you can use any package that implements the log::Log trait.

Info level logging helps to inspect how a feature flag was evaluated:

INFO [5000] Evaluating 'isPOCFeatureEnabled' for User '{"Identifier":"<SOME USERID>","Email":"[email protected]","Country":"US","SubscriptionType":"Pro","Role":"Admin","version":"1.0.0"}'
  Evaluating targeting rules and applying the first match if any:
  - IF User.Email CONTAINS ANY OF ['@something.com'] THEN 'false' => no match
  - IF User.Email CONTAINS ANY OF ['@example.com'] THEN 'true' => MATCH, applying rule
  Returning 'true'.

As an example, this sample app defines a minimal log::Log implementation that uses println!() to show log messages on the console.

Sample Applications

Check out our Sample Applications how they use the ConfigCat SDK:

Sample App

Getting started​

1. Install the package​

2. Import the configcat module to your application​

3. Create the ConfigCat client with your SDK Key​

4. Get your setting value​

Creating the ConfigCat Client​

Custom client options​

Anatomy of get_value()​

Setting type mapping​

Anatomy of get_value_details()​

User Object​

User Object Attribute Types​

Default user​

Polling Modes​

Auto polling (default)​

Lazy loading​

Manual polling​

Online / Offline mode​

Flag Overrides​

JSON File​

File​

JSON File Structure​

1. Simple (key-value) structure​

2. Complex (full-featured) structure​

Map​

get_all_keys()​

get_all_values()​

get_all_value_details()​

Cache​

HTTP Proxy​

HTTP Timeout​

Logging​

Sample Applications​

Look under the hood​

Getting started

1. Install the package

2. Import the `configcat` module to your application

3. Create the ConfigCat client with your SDK Key

4. Get your setting value

Creating the ConfigCat Client

Custom client options

Anatomy of `get_value()`

Setting type mapping

Anatomy of `get_value_details()`

User Object

User Object Attribute Types

Default user

Polling Modes

Auto polling (default)

Lazy loading

Manual polling

Online / Offline mode

Flag Overrides

JSON File

File

JSON File Structure

1. Simple (key-value) structure

2. Complex (full-featured) structure

Map

`get_all_keys()`

`get_all_values()`

`get_all_value_details()`

Cache

HTTP Proxy

HTTP Timeout

Logging

Sample Applications

Look under the hood